Organizations that use information technology increasingly operate in a challenging environment of accelerating change and disruption. Increasingly adaptive enterprises meet these challenges by using information technology infrastructures that function in the manner of utilities in which the service provided, rather than the components performing the service, is the most important factor in configuring a system.
In an adaptive enterprise, information technology service levels match the flow of real-time business activities using low-cost, dependable, reliable, and scalable services that are available and dynamically-mapped to meet needs during peak activities and lulls. To operate proficiently as an adaptive enterprise, information technology services can respond rapidly to changing internal and external business circumstances, supplying continuous, secure computing and storage services that are protected and optimized using automated, intelligent management operations and a capability to discover, allocate, optimize, and de-allocate resources including servers, network components, storage elements, and application services from predefined “pools” of components.
Resource virtualization is the abstraction or virtualization of server, storage, and network resources to attain dynamically available resources for sharing by information technology services both inside and outside an organization without disturbing or disrupting access to data of other applications. Server virtualization enables horizontally and vertically scaled server environments, enabling optimized utilization, improved service levels, and reduced management overhead. Network virtualization is enabled by intelligent routers, switches, and other networking elements supporting virtual local area networks (LANs). Virtualized networks increase security and can support unforeseen spikes in customer and user demand. Storage virtualization can be based in servers, networks, or arrays and improves utilization of storage subsystems, reduces administration costs, and protects valuable data.
A system is virtualized by separating logical functions of the server, storage, and network elements from physical functions. For example, all servers, storage, and network devices can be aggregated into independent pools of resources. Some elements may even be further subdivided, for example into server partitions, storage logical units (LUNs), and the like, to give an even more granular level of control. Elements from resource pools can be allocated, provisioned, and managed—either manually or automatically, to adapt to changing needs and priorities of business.
In a system using storage virtualization, pooling of physical resources is enabled at various levels in a storage hierarchy. In array controllers, virtualization allows physical capacity to be allocated more efficiently and dynamically. Virtualization of networked storage enables higher availability, better utilization, and centralized management of network storage device groups such as Storage Area Network (SAN)-attached array controllers or network-attached storage (NAS) files servers. Server-based utilization pools physical capacity for both SAN and direct-attached storage (DAS) within the context of a single server.
Storage virtualization involves formation of an abstraction layer between physical storage devices and logical volumes consumed by applications. Abstraction hides details of the storage infrastructure from servers, simplifying the overall management environment. Resource pooling hides physical details of data location, creates subsets of resources for protection, and aggregates resources for higher bandwidth, capacity, and/or availability. Virtualization abstracts storage capacity by mapping storage capacity providing elements, such as physical devices or logical units (LUNs), into a logical space, and creating logical devices that are presented to applications, erasing physical boundaries, creating pools of capacity that can be managed and accessed according to need.
Storage virtualization simplifies storage management by automating addition, allocation, and re-allocation of storage resources to the infrastructure. Storage virtualization also improves storage utilization by ensuring that an appropriately configured storage environment maps to the application and data requirements. Virtualization also relieves the burden of significant pre-allocation of storage capacity to meet growing or peak demands. Storage virtualization also enables storage services across heterogeneous environments, resulting in simplified management and improved utilization of existing resources.
Many conventional primary storage systems use disk arrays to assure high availability of data. Primary data transfer and processing capability in the array resides on one or more controllers. Some systems are moderate in size with exactly two controllers for fault tolerance. Other systems have larger arrays with more than two controllers for higher performance. Unfortunately, arrays with many controllers tend to have a much higher entry cost than smaller, more modular arrays.
As system capacity or performance requirements increase, a common upgrade is growth from two or more controller systems to larger systems without downtime. Growth occurs when either performance or capacity demands exceed the capability of one controller pair or array. A common expansion involves the addition of controllers or arrays to a datacenter and, if necessary, moving data between arrays to balance work across controllers. Data movement is imposed to balance load across controller pairs because each disk is directly connected to at most two controllers within one array.
One problem of conventional storage arrays in which each disk is connected to exactly two controllers is that the association of disk to controller pair cannot be changed. The controller/disk combination is unable to adapt to change without data movement that consumes both time and resources. Expansion of controller resources to relieve performance bottlenecks generally demands addition of disks, as well as additional controllers. Since disks have a restrictive physical association with one controller pair, bottlenecks cannot be alleviated in the controller pair without moving data. Data movement, while potentially on-line, consumes time and resources, therefore unsuitable as a response to frequent, periodic, or short-term performance or capacity burdens. Consequently, a storage system has difficulty responding to growth beyond a single array. Furthermore, the storage system, in the event of a failed controller or controllers, has difficulty sustaining performance and availability. Also, the storage system cannot easily optimize performance for periodic changes in demand.